The present invention relates to the field of electronic imaging devices, and more particularly to a means and method for testing essential components of liquid crystal on silicon (xe2x80x9cLCOSxe2x80x9d) imaging devices. The predominant current usage of the present inventive improved testability method and apparatus is in the production of reflective liquid crystal display (xe2x80x9cLCDxe2x80x9d) imaging devices, wherein the early detection of defective silicon components would be most desirable.
A known type of LCOS display utilizes pixel mirrors to project images. These mirrors act as electrodes to modulate reflected light. These pixel mirrors contain an electrical contact that is connected to a data source, such as an analog multiplexer (xe2x80x9cmuxxe2x80x9d). During the manufacturing process production errors can occur such that one or more of the mirrors might not achieve a good electrical contact, resulting in an unconnected mirror. Currently, pixel mirrors are inspected at final completion visually. When unconnected mirrors are detected the entire assembly is discarded.
Ideally, unconnected mirrors would be detected before they proceed through the entire liquid crystal assembly. This would save the effort and expense of finishing the processing of such assemblies, and would significantly decrease the average overall cost of the production of such devices. It would also be advantageous to have a method or means to test the electrical properties of the LCOS display by some less labor-intensive method than the visual inspection method now common in the art. However, to the inventor""s knowledge, no such method or means has existed in the prior art. Current practice is to rely on visual inspection utilizing different test patterns to make sure every cell is working properly.
Aside from the problem of improper electrical connections, there also exists a possibility of other problems occurring during the wafer manufacturing process in which the logic of the integrated circuitry might become corrupted. Such defects also result in the entire assembly being discarded. This makes finding a method or means for detecting errors before these defective imaging devices complete the entire liquid crystal assembly even more desirable. However, to the inventor""s knowledge no method or means has existed in the prior art to easily and reliably detect such defects.
It is an object of the present invention to provide a method for electrically detecting unconnected mirrors of LCOS imaging devices.
It is another object of the present invention to provide a method and apparatus for testing the internal logic of an LCOS imaging device.
It is still another object of the present invention to provide a method and apparatus for reducing the cost of production of LCOS imaging devices.
It is yet another object of the present invention to provide a method and apparatus for producing high quality LCOS imaging devices.
It is yet another object of the present invention to provide a method and apparatus wherein unconnected mirrors in an LCOS imaging device can be detected before they proceed through liquid crystal assembly, thereby allowing the mirror to be discarded before resources are used unnecessarily.
It is still another object of the present invention to provide a method and apparatus that allows for detection of unconnected mirrors before the entire liquid crystal assembly of an LCOS imaging device is completed.
It is yet another object of the present invention to provide a method and apparatus for easily detecting electrical faults in an LCOS imaging device.
Briefly, the present invention introduces a single transistor (a mirror read pass transistor) into the driver circuitry of an imaging device, for the purpose of detecting unconnected pixel mirrors. According to the present invention, the pixel mirror has two electrical contacts, one connected to the output of an analog mux and the other to a mirror read pass transistor. The placement and configuration of the mirror read pass transistor allows for the reading of the mirror voltage electronically, thus allowing for the detection of unconnected mirrors. The introduction of the mirror read pass transistor also provides a method and means for detecting electrical faults in electrical driver circuitry, such as a slave cell and an analog mux cell.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of modes of carrying out the invention, and the industrial applicability thereof, as described herein and as illustrated in the several figures of the drawing. The objects and advantages listed are not an exhaustive list of all possible advantages of the invention. Moreover, it will be possible to practice the invention even where one or more of the intended objects and/or advantages might be absent or not required in the application.
Further, those skilled in the art will recognize that various embodiments of the present invention may achieve one or more, but not necessarily all, of the above described objects and advantages. Accordingly, the listed advantages are not essential elements of the present invention, and should not be construed as limitations.